Hydantoin racemase is an enzyme that acts upon optically active 5-substituted hydantoin compounds, or more specifically D- or L-5-substituted hydantoin compounds to catalyze the racemization reaction of these compounds. The enzyme can therefore be used for the production of optically active N-carbamylamino acid or optically active amino acid, which is important as a source material of pharmaceuticals, chemical produces, and food additives, using a 5-substituted hydantoin compound as a starting material.

As shown in Formula (I), in order to produce optically active N-carbamylamino acid from a 5-substituted hydantoin compound, hydantoin racemase is used with hydantoinase having stereoselectivity. In order to produce optically active amino acid from a 5-substituted hydantoin compound, hydantoin racemase is used with hydantoinase having stereoselectivity, as well as N-carbamylamino acid amidohydrolase having or not having stereoselectivity.
The enzyme reactions by hydantoinase and N-carbamylamino acid amidohydrolase may be separately performed in two steps, or alternatively the two enzymes may be mixed together to perform the two reactions in one step.
The decarbamylation reaction following the hydantoinase reaction may alternatively be performed using a decarbamylation method employing conventionally well-known chemical reactions, other than the foregoing method using enzyme.
In the method of reaction using hydantoinase and N-carbamylamino acid amidohydrolase, performing the racemization of the starting 5-substituted hydantoin compound concurrently with the hydantoinase reaction using hydantoin racemase enables the 5-substituted hydantoin compound to be quantitatively converted into optically active N-carbamylamino acid or optically active amino acid, with the result that yield is increased.
Meanwhile, there have been known 5-substituted hydantoin compounds that undergo chemical racemization in the foregoing reaction system. However, they are only limited kinds of such compounds. Further, in many of such 5-substituted hydantoin compounds, the chemical racemization proceeds either slowly or does not proceed at all in practice. As such, a high yield cannot be expected when hydantoin racemase is not used. It is therefore very meaningful to use hydantoin racemase in the present reaction system. Accordingly, a search is underway for hydantoin racemase in order to facilitate racemization of optically active 5-substituted hydantoin compounds, which can be racemized only slowly.
As examples of microorganisms that can produce hydantoin racemase, the microorganisms of the following Genus are known: Arthrobacter; (Patent Publication 1, Non-Patent Publication 1); Pseudomonas (Patent Publication 2, Non-Patent Publication 2); Agrobacterium (Non-Patent Publication 3, Non-Patent Publication 4, Patent Publication 3); Sinorhizobium (Non-Patent Publication 5); Microbacterium (Patent Publication 4); Flavobacterium (Patent Publication 5); Pasteurella (Patent Publication 6); Candida (Patent Publication 7).
[Patent Publication 1]    Japanese Laid-Open Patent Publication No. 122591/1987 (Tokukaisho 62-122591)
[Patent Publication 2]    Japanese Laid-Open Patent Publication No. 271784/1992 (Tokukaihei 4-271784)
[Patent Publication 3]    PCT International Publication No. WO03/100050
[Patent Publication 4]    Japanese Laid-Open Patent Publication No. 330784/2002 (Tokukai 2002-330784)
[Patent Publication 5]    Japanese Laid-Open Patent Publication No. 210176/2003 (Tokukai 2003-210176)
[Patent Publication 6]    Japanese Laid-Open Patent Publication No. 210177/2003 (Tokukai 2003-210177)
[Patent Publication 7]    Japanese Laid-Open Patent Publication No. 47194/1986 (Tokukaisho 61-47194)
[Non-Patent Publication 1]    J. Biotechnol., vol. 80, 217 (2000)
[Non-Patent Publication 2]    J. Bacteriol., vol. 174, 7989 (1992)
[Non-Patent Publication 3]    Appl. Microbiol. Biotechnol., 57, 680 (2001)
[Non-Patent Publication 4]    Biotechnol. Prog., 18, 1201 (2002), Biochem. Biophys. Res. Commun. 303, 541 (2003)
[Non-Patent Publication 5]    Appl. Microbiol., 70, 625 (2004)